The invention lies in the field of semiconductor manufacture. More specifically, the invention relates to a semiconductor structure having a layer structure formed from a metalization layer and a dielectric layer. The metalization layer is patterned and has contact areas, and the dielectric layer is composed of a depositable material and covers the metalization layer. Such a semiconductor structure is disclosed, for example, in published Japanese patent application JP 9-289247.
Layer structures of that type are present in many modern semiconductor structures in which components arranged on the substrate surface are connected to one another by a plurality of metal layers lying above them. The metal layers in such multilayer metalizations are insulated from one another by interposed dielectric layers. The interconnect structures of the individual metal planes are connected to one another by so-called vias, for which purpose contact areas are formed in the metal planes. These contact areas are wider than the interconnects themselves and are usually arranged at the edge of the semiconductor structure below bonding pads.
A respective dielectric is deposited as ILD (interlevel dielectric layer) over the patterned metalization planes. The use of inductively coupled high density plasma (HDP) has proved successful for the deposition. Narrow trenches between metalization tracks are also reliably filled thereby without any gaps. In the course of deposition with the aid of the HDP method, elevations of the dielectric are produced over the metalization tracks. These elevations cannot be completely eliminated using planarization methods such as chemical mechanical polishing CMP and thus form fault sources for subsequent process steps. By way of example, coupling capacitances that are difficult to predict arise between adjacent metalization planes. The behavior of the semiconductor structure on carrying out analog functions becomes less predictable. The performance of lithographic techniques is also limited. In particular, DUV lithography in conjunction with metal etching by means of reactive ions (reactive ion etching; RIE) requires high planarity of the dielectric layers.
The dielectric elevations that occur are particularly high over large-area regions of the underlying metalization layer. In particular contact areas, serving, for instance, to interconnect the metalization planes, are covered by a dielectric layer having the full deposition thickness. In contrast to the narrower interconnects, which are covered by a comparatively low wall of the dielectric, the size of the contact areas cannot be arbitrarily reduced because the vias that are to be introduced over them into the dielectric must be connected unerringly to the contact area despite any exposure faults.
Therefore, the dielectric is deposited on the comparatively large contact area with the same deposition thickness as between the interconnects. The resulting elevations lead to the above-mentioned disadvantages.
The object of the invention is to provide a semiconductor structure which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and wherein these elevations are largely avoided without the size of the contact areas having to be reduced and the latter then leading to fault sources in the course of via contacting. p With the above and other objects in view there is provided, in accordance with the invention, a semiconductor layer structure, comprising:
a patterned metalization layer having contact areas formed of a plurality of contiguous individual structures;
a dielectric layer formed of deposited material covering the metalization layer;
the individual structures of the contact areas having a width reduced to such a degree that the deposited material does not form, over the individual structures, any areas running parallel to the metalization layer.
In other words, the objects of the invention are achieved by forming the-contact areas from many contiguous individual structures, and that the individual structures are so narrow that the depositable material does not form, over the individual structures, any areas which run parallel to the metalization layer. Each elevation over a metalization web has two inclined sidewalls, which, in the case of narrow webs, converge above the center thereof or, in the case of wide webs, bound a surface which is parallel to the substrate and the metalization plane. The height of this surface above the web corresponds to the deposition thickness. The invention exploits the fact that narrow webs are covered by roof-shaped elevations which are shallow in comparison with the deposition thickness. If the conventionally solid contact area is formed by a grid or network of contiguous individual structures, for instance lines, then the trenches or openings in between are filled with the dielectric. The contact-hole-forming grid of interconnects is covered merely by a shallow grid of low elevations of the dielectric, which are easier to planarize than solid elevations and, under certain circumstances, need not be removed on account of their small height. Since the individual structures are contiguous, the function of the grid as contact area remains unimpaired.
The additional width of the individual structures is determined by the angle between the sidewalls of the elevations and the substrate metalization plane. According to the invention, the individual structures are so narrow that the sidewalls of the elevations of the dielectric abut one another and are thus lower than the thickness with which the dielectric is deposited over trenches.
In accordance with an added feature of the invention, the dielectric layer is deposited between the individual structures at a given deposition thickness, and the width of the individual structures is less than twice the given deposition thickness. This limiting width corresponds to a sidewall angle of 45xc2x0. A further embodiment provides for the width of the individual structures to correspond to the structure width with which the semiconductor structure is fabricated. As a result, the elevations over the contact areas are kept as low as possible.
Further embodiments directed at the grid structure of the contact areas provide for the individual structures to form a grating of parallel line structures or a network of intersecting line structures.
The dielectric layer is preferably a layer deposited by means of a high density plasma. The metalization layer preferably contains aluminum or else copper.
In accordance with another feature of the invention, further layer structures comprising metalization layers and dielectric layers are arranged above and/or below the above-noted layer structure. The metalization layers form a multilayer metalization configuration. The contact areas of the metalization layers are preferably arranged below bonding pads. In a preferred embodiment, the semiconductor structure is an embedded DRAM.
The individual planes of a multilayer metalization configuration are connected by means of the vias introduced into the interposed dielectric layers. The contact areas are generally situated at the edge of a semiconductor substrate, generally below bonding pads. With this arrangement, the invention affords the additional advantage that continuous oxide supports reaching as far as the substrate are formed below the bonding pads (which are formed by the topmost metalization layer and therefore need not be patterned). In conventional semiconductor structures, below the bonding pads, due to the alternate sequence of solid metal contact areas and oxide layers, there is the risk of breaking under the pressure of the bonding wire to be emplaced. Even when test needles are placed onto the individual contact areas for test purposes, cracking often occurs under the pressure of the test needle. By virtue of the dielectric-filled contact areas patterned according to the invention, the pressure is transmitted through the contact areas to the substrate; fractures no longer occur. The use of the present invention is appropriate particularly in the case of embedded DRAMs, which, under certain circumstances, have a few hundred bonding pads with contact area stacks situated underneath.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a patterning of contact areas in multilayer metalization configurations of semiconductor components it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.